The present invention relates to a method of recording a densitogram representing densities of fractionated substances contained in a sample.
For instance, in an electrophoretic apparatus for analyzing various proteins in a serum sample, there is formed a densitogram representing fraction curves of albumin (Alb), alpha-1-globulin (.alpha..sub.1), alpha-2-globulin (.alpha..sub.2), beta-globulin (.beta.) and gamma-globulin (.gamma.), fraction percentages of these protein substances, and a ratio (A/G) of albumin to total globulin. By means of such data, it is possible to know a relative change in density of the protein substances. Recently, in addition to such a relative change in density, an absolute change in density of the substances has become important. In order to satisfy such a request, absolute values of density of the substances are obtained by deriving products of respective fraction percentages and a total density of the whole protein which is separately measured by the known refraction method or colorimetric method.
For instance, a protein composition of a patient shown in FIG. 1 is changed into that illustrated in FIG. 2 by any reason. It can be seen from FIGS. 1 and 2 that the fraction percentage of Alb is decreased by about 0.75 times and the fraction percentages of .alpha..sub.1 -, .alpha..sub.2 -, .beta.- and .gamma.-globulins are increased by 1.5 times. Then, the change in protein composition can be accurately known from the absolute protein density values which are obtained by multiplying respective fraction percentages with the total protein density.
However, in case of recording the densitogram, an automatic span control is utilized in such a manner that a peak value of the albumin fraction having usually the highest density is brought into a given constant level and the fractions of globulins are recorded relative to the albumin fraction. Then, densitograms shown by curves I and II in FIG. 3 are formed for the protein compositins illustrated in FIGS. 1 and 2, respectively. From these curves, the fractions of .alpha..sub.1 -, .alpha..sub.2 -, .beta.- and .gamma.-globulins seem to increase although the densities of these globulins are not changed at all and the density of albumin is decreased by two times.
It has also been known to record the densitogram without effecting the automatic span control. In this case, the densitogram can correctly represent the density change of the proteins as long as amounts of serum samples are equal to each other. However, in practice, it is very difficult to apply uniformly a given constant amount of samples to sample bearing films to be used in the electrophoresis. If amounts of samples applied to the bearing films are different from each other, the change in density of the proteins cannot be correctly known from the densitograms.